1. Field of the Invention
The present invention relates to an electromagnetic relay.
2. Description of the Related Art
Conventionally, in an electromagnetic relay used for applications in which a number of circuit components should be arranged in a limited space, such as applications for vehicle-mounted electric appliances or audio equipment, it is required to inhibit an increase in the manufacturing cost and to facilitate miniaturization. In this type of electromagnetic relay, as the outer dimensions thereof are further reduced, it tends to be difficult to assemble components, such as an electromagnet, a contact section, etc., with a high positional accuracy.
For example, Japanese Unexamined Patent Publication (Kokai) No. 2002-100275 (JP-A-2002-100275) discloses an electromagnetic relay in which an electromagnet (including a coil, a bobbin, an iron core and a yoke) and a contact section (including a stationary contact and a movable contact) operable to open or close with an operation of the electromagnet are fitted to a common base, and in which a stationary contact member having the stationary contact is fixedly supported on the base and a movable contact-spring member having the movable contact is supported on the electromagnet in an elastically displaceable manner. In this configuration, the fitting accuracy of the electromagnet with respect to the base affects a positional correlation between the stationary contact and the movable contact. More specifically, if the position of the electromagnet deviates on the base, the movable contact deviates from a proper position relatively to the stationary contact and, as a result, the operational characteristics of the electromagnetic relay may become unstable. Therefore, for example, in the electromagnetic relay as set forth in JP-A-2002-100275, a leg formed on the bobbin of the electromagnet is inserted into a hole formed in the base and a catch formed at the distal end of the leg is engaged with the bottom face of the base and, thereby, the electromagnet is fixed at a predetermined position on the base.
On the other hand, Japanese Unexamined Patent Publication (Kokai) No. 10-3841 (JP-A-10-3841) discloses an electromagnetic relay having the common base described above, in which not only the stationary contact member but also the movable contact-spring member is supported on the base. This configuration typically uses a transmission member (referred to as, e.g., a card) for transmitting the operation of the electromagnet to the movable contact-spring member. In this configuration, if the position of the electromagnet deviates on the base, a positional correlation between the transmission member and the movable contact-spring member is changed and, as a result, the operational characteristics of the electromagnetic relay may also become unstable. Therefore, for example, in the electromagnetic relay as set forth in JP-A-10-3841, a support section is formed on the base to fixedly support, in an engaging manner, the yoke of the electromagnet at a predetermined position. The support section is provided with a guide groove for slidably receiving the outer periphery of the yoke and a slit for holding a local projection formed on the outer periphery of the yoke under elastic pressing force. In an action of fitting the electromagnet to the base, the guide groove of the support section is slidably engaged with the outer periphery of the yoke so as to guide the electromagnet in a fitting direction parallel to a coil center axis.
In the electromagnetic relay as set forth in JP-A-2002-100275, the leg formed on the bobbin of the electromagnet is inserted into the hole formed in the base, so that the electromagnet is fixed at the predetermined position on the base. In this configuration, as the electromagnetic relay is further miniaturized, it tends to become difficult to insert the leg of the bobbin into the hole of the base. Moreover, in order to ensure the positional fitting accuracy of the electromagnet with respect to the base, it is necessary to improve the molding dimensional accuracy of the small-sized leg and hole, which may result in an increased manufacturing cost.
On the other hand, in the electromagnetic relay as set forth in JP-A-10-3841, the outer periphery of the yoke of the electromagnet is inserted into the guide groove formed in the support section of the base, so that the electromagnet is fixed at the predetermined position on the base. In this configuration, as the electromagnetic relay is further miniaturized, it tends to become difficult to insert the outer periphery of the yoke into the guide groove of the support section. In particular, due to the fact that the positional fitting accuracy of the electromagnet with respect to the base is ensured by the slit of the support section holding the local projection of the yoke under an elastic pressing force, the positional deviation of the electromagnet may occur if an external force larger than the elastic pressing force is applied to the electromagnet. Further, the configuration having the card exhibits a poor continuous-current performance (e.g., of 25 A) required for a vehicle-mounted application and thus is not suitable for a vehicle-mounted use.